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https://github.com/mefellows/pact-foobar-plugin

Pact plugin tutorial
https://github.com/mefellows/pact-foobar-plugin

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Pact plugin tutorial

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README 

        
# Pact Plugin Template



Template project to help bootstrap a new Pact [Plugin](https://github.com/pact-foundation/pact-plugins) for the [Pact](http://docs.pact.io) framework. 



**Features:**



* Stubbed gRPC methods ready to implement

* Automated release procedure

* Support for recommended common platform/targets

* Levelled logging for observability



**TODO**



- [ ] Support Matchers and Generators (requires FFI package support)



## Repository Structure



```

├── go.mod            # Go module                              (✅ fill me in!)

├── main.go           # Entrypoint for the application

├── plugin.go         # Stub gRPC methods for you to implement (✅ fill me in!)

├── configuration.go  # Type definitions for your plugin's DSL (✅ fill me in!)

├── Makefile          # Build configuration                    (✅ fill me in!)

├── io_pact_plugin/   # Location of protobuf and gRPC definitions for Plugin Framework

├── log.go            # Logging utility

├── pact-plugin.json  # Plugin configuration file

├── pact.go           # Pact type definitions

├── server.go         # The gRPC server implementation

├── RELEASING.md      # Instructions on how to release 🚀

```



## Developing the plugin



### Prerequsites



The protoc compiler must be installed for this plugin 



### Create your new repository



1. Clone this repository 

2. Create a new repository in GitHub. The name of the plugin should be `pact--plugin` e.g. `pact-protobuf-plugin`

3. Push this code to your new repository



### Update the Go module name



Replace `github.com/pact-foundation/pact-plugin-template-golang` in [`go.mod`](./go.mod) with your github URL (without the protocol prefix) to identify the package uniquely.



Similarly, correct the import at the top of [`plugin.go`](./plugin.go) and [`server.go`](./server.go).



Or simply do a workspace wide search and replace from `github.com/pact-foundation/pact-plugin-template-golang` to your go module name.



### Set the name and version



In the top of the [`Makefile`](./Makefile) set `PROJECT` to your plugin's name.



`PROJECT` should map to `` in your GitHub repository.



*NOTE: It's important that the name of your go module and the `PROJECT` variable must align, to create artifacts discoverable to the CLI tooling, such as the [Plugin CLI](https://docs.pact.io/implementation_guides/pact_plugins/cli).*



### Design the consumer interface



This is how the users of your plugin will write the plugin specific interaction details. 



For example, take the following HTTP interaction:



```js

await pact

  .addInteraction()

  .given('the Matt protocol exists')

  .uponReceiving('an HTTP request to /matt')

  .usingPlugin({

    plugin: 'matt',

    version: '0.0.4',

  })

  .withRequest('POST', '/matt', (builder) => {

    builder.pluginContents('application/matt', mattRequest); // <- request

  })

  .willRespondWith(200, (builder) => {

    builder.pluginContents('application/matt', mattResponse); // <- response

  })

  .executeTest((mockserver) => {

          ...

```          



The user needs to specify the request and response body portion of the request.



Because the use cases for plugins are so wide and varied, the framework does not impose limits

on this data structure and is something you need to design.



This being said, most plugins have opted to use a JSON structure. 



This structure should be represented in [`configuration.go`](./configuration.go)



Think about how you would like your user to specify the interaction details for the various interaction types. 



Here is an example for a TCP plugin with a custom text protocol:



#### Synchronous Messages



Set the expected response from the API:



```go

mattMessage := `{"response": {"body": "hellotcp"}}`

```



#### Asynchronous Messages



Set the request/response all in one go:



```go

mattMessage := `{"request": {"body": "hellotcp"}, "response":{"body":"tcpworld"}}`

```



#### HTTP



Separate out the body on the request/response part of the interaction:



```go

mattRequest := `{"request": {"body": "hello"}}`

mattResponse := `{"response":{"body":"world"}}`

```



### Write the Plugin!



#### Implement the relevant RPC functions



Open [`plugin.go`](./plugin.go) and update the relevant RPC functions. 



Depending on your use case, some of the RPC calls won't be required, each method is well signposted to help you along.



#### Logging



You should log regularly. Debugging gRPC calls from the framework can be challenging, as the plugin is started asynchronously by the Plugin Driver behind the scenes.



There are two ways to log:



1. Stdout - all stdout (e.g. `fmt.Print*`) is pulled into the general Pact logs for the framework you're running

2. To file. All calls to `log.Print*` will be written to file



The log setup has three main features:



1. It works with the native Go `log` package

2. It logs to a file relative to plugin execution in `log/plugin.log`

3. It is levelled, at the direction of the plugin driver (that is, the log level will pass in from the driver which will restrict the levels logged in this plugin)



To write something to the log file, you simply use the `log` package, with the level prefixed as per below:



```golang

log.Println("[TRACE] ...")

log.Println("[DEBUG] ...")

log.Println("[INFO] ...")

log.Println("[WARN] ...")

log.Println("[ERROR] ...")

```



### Publish your plugin



Follow the steps in [Releasing](./RELEASING.md) to publish a new version of your Plugin. 



## Local Development



The following command will build the plugin, and install into the correct plugin directory for local development:



```

make install_local

```



You can then reference your plugin in local tests to try it out.



### Regenerating the plugin protobuf definitions



If a new protobuf definition is required (e.g. to support a new feature), copy into the `io_pact_plugin` folder and run the following Make task:



```

make proto

```



It will update the definitions in the `io_pact_plugin` package. Note this may result in a breaking change, depending on the version. So upgrade carefully.



## Supported targets



This code base should automatically create artifacts for the following OS/Architecture combiations:



| OS      | Architecture | Supported |

| ------- | ------------ | --------- |

| OSX     | x86_64       | ✅         |

| OSX     | arm          | ✅         |

| Linux   | x86_64       | ✅         |

| Linux   | arm          | ✅         |

| Windows | x86_64       | ✅         |

| Windows | arm          | ✅         |